The invention concerns a method for the production of brushes, consisting of a bristle support and bristles of at least two different bristle types which are fastened thereto and combined to at least one group having a defined cross-section by uniting the bristles of one bristle type to form a partial group and the partial groups forming the bristle group are combined in converging guides to form the bristle group, wherein the bristle group is subsequently attached to the bristle support. The invention also concerns a device for carrying out the method.
Conventional brushes consist of a bristle support and bristles fastened thereon which are usually combined to form bristle groups, e.g. bundles. The bristle groups are mounted to the bristle support either mechanically, using the so-called punching method, or, if the bristles and bristle supports are made from plastic, more recently using a thermal process, in optional combination with a mechanical deformation method. Such recent methods include welding of the bristles onto the surface of the bristle support, inserting the bristle bundles into a bristle support surface which is melted to a greater or lesser extent or injection molding the bundle by melting the bristle ends at the bundle foot to form an enlargement and extruding bristle support material around this area. These thermal methods have been used, in particular, for tooth brushes, hygiene brushes etc.
The selection of bristles with regard to material, cross-section and length depends largely on the intended use of the brush. The arrangement and number of bristles in a bundle, the arrangement and shape of the bundles themselves or of the bristles which are combined into groups vary in dependence on the intended use. The term brushes also includes brush-like devices for applying media, wherein the bristles are generally disposed in one group only, i.e. a bundle, a package or the like.
As has been known in the art for some time, tooth brushes having a straight cut brush stock, i.e. with all bristle ends disposed in one plane, do not satisfy dental hygienic requirements, since the curved as well as uneven tooth surfaces and the interdental spaces are not adequately cleaned. For these reasons, tooth brushes were developed having bristle ends lying in envelope surfaces contoured to a greater or lesser degree, by e.g. providing the bristle stock with a wavy cut. There are also conventional brushes which have the ends of bristles of an individual bundle disposed on a conical surface. All these measures are intended to assure that the bristles reach into the interdental spaces.
Dental medical evaluations of such tooth brushes have, however, shown that the tips of individual bundles or the apex of a wavy cut are unacceptably aggressive on the smooth tooth surfaces and leave grinding traces on the enamel. They can also lead to injury of the gum and gingiva which causes discomfort, especially with sensitive gums.
These disadvantageous consequences can be alleviated, but not eliminated, by a conventional tooth brush (WO 96/16571). Its bristle stock consists of individual bundles whose ends lie in a conical surface having the above mentioned aggressive tip. Moreover, each bundle contains individual bristles which are longer than the other bristles in the bundles and whose ends are disposed in one single plane. These individual bristles thereby slightly protrude past the bundled bristles. This configuration is intended to improve cleaning of the interdental spaces, since the individual bristles can more easily access such areas compared to conical bundles. These brushes are difficult to manufacture, since the individual bristles have to be drawn into the bundles in a separate processing step.
Macroscopic studies have shown that the tooth surfaces have fine cracks into which conventional bristles, due to their diameter, cannot enter and which are therefore not cleaned. Thinner, fiber-like bristles (DE 94 08 268 U1) which are wrapped in an enclosed envelope, with only the ends protruding past the wrapping, were proposed for cleaning and gentle treatment of the gums. These thin fibers fold down outside the wrapping envelope and have almost no effect. In addition, the sharp envelope edge increases the danger of injury to the gums and gingiva as well as possible damage to the tooth surface due to grinding traces. This conventional tooth brush is also very difficult to manufacture.
With tooth brushes and also with other brushes, such as paint brushes and the like, the bristle groups must be arranged in defined geometrical shapes and different types of bristles must be inserted into the bristle stock or individual bristle groups forming same to achieve the effects required for the respective application. DE 16 04 673 discloses bundles having differing cross-sectional shapes and DE 35 05 972 discloses combining the bristle stock of differently shaped bundles. These different bundle shapes are generated by rolling endless monofilaments to form a cord, wherein each cord consists of a number of monofilaments corresponding to the number of bristles in a bundle. The monofilament cord is pulled or pushed through a shaping device which forms the cord, of irregular cross-sectional shape, into the desired cross-sectional shape. Downstream of the shaping device, the bundles are cut to the desired length and fastened to the bristle support. This only allows variation of the bundle shape.
DE 196 16 309 suggests the production of bundles of bristles of different types by winding together endless monofilaments of various types to form a cord, from which individual bundles are cut. In this case, different types of bristles are present within the bundle in a static, uniform distribution. The various bristles are not distributed and arranged in dependence on the application. EP-A1-0 716 821 discloses tooth and body care brushes with which the bristles are collected into groups containing different kinds of bristles.
In conventional brushes having injection molded bundles (U.S. Pat. No. 5,728,408) the bristles, cut to bundle length, are removed from a magazine using punching tubes and inserted in bundle channels of an injection molding form and into the mold cavity. Several bundles of circular cross-section can thereby be combined via converging channels, next to one another, into stripe-shaped bristle groups having a width corresponding to the bundle diameter. Neighboring bundles may comprise various bristles disposed next to one another in the stripe-shaped bristle group. The various types of bristles thereby disadvantageously mix in the transition area between neighboring bundles and are not effective in this area. Since bristles of various types are adjacent to one another in the stripe-shaped bristle group and are used in the same manner during brushing, both types of brushes display differing signs of premature wear.
It is the underlying purpose of the invention to further develop the conventional method of U.S. Pat. No. 5,728,408 according to the preamble of claim 1 in such a manner that brushes can be produced in any form and in dependence on the intended use which have bristle groups consisting of partial groups of various cross-sections, with bristles of different types and different numbers in the partial groups.
This object is achieved in accordance with the invention in that the bristles of each partial group are shaped in a surrounding shaping device guide to obtain a cross-section corresponding to their partial cross-section in the bristle group and the partial groups are then combined in the guides to obtain the cross-sectional shape of the bristle group. Preferably, the bristle group is then transferred to a holding means to transport the bristle group for fastening to the bristle support. The finished bristle group can also be attached to the bristle support directly after shaping.
The method according to the invention permits production of a bristle group of defined cross-section from partial groups of various bristle types also having defined partial cross-sections such that the various types of bristles are present within the bristle group in a defined geometrical shape optimally adapted to the respective use of the brush. With this geometrical shape generated by the shaping device, the bristle groups or the partial groups forming same may be subsequently fixed in the holding means and fastened to the bristle support using conventional mechanical or thermal methods while maintaining this geometrical shape. The inventive method can generate bristle groups of arbitrary cross-section within which the partial groups of arbitrary cross-section are arranged to always optimize the respective intended use. The partial groups may thereby be arranged e.g. concentrically, in the form of segments, sectors or stripes. The invention permits different numbers of bristles to be used in each partial group.
Preferably, the bristles of each partial group are compressed during shaping into close proximity to one another and support each other within the partial group. This dense packaging of bristles is particularly advantageous for thermal fastening of the bristle group on the bristle support, since the softened plastic mass of the bristle support cannot enter between the bristles.
With the method in accordance with the invention, all groups of bristles in the bristle stock of the brush can be simultaneously or sequentially formed in the shaping device. In either event, they can be passed on to a holding means accepting all bristle groups for attaching the complete bristle stock to the bristle support.
In a preferred embodiment, the partial groups, after being combined to form a bristle group, are transferred, with different lengths, to the holding means and are cut flat at a location between the shaping device and the holding means.
This allows the useful ends of the partial groups forming the bristle groups to be disposed in different planes such that their different characteristics can be simultaneously effective during brushing.
The bristle groups are preferably clamped in the holding means to fix the geometrical shape generated by the shaping device.
This allows, in particular, the useful ends of the bristles of the bristle groups clamped in the holding means to be mechanically treated, e.g. rounded, and also facilitates preparation of their opposite ends for mounting to the bristle support: e.g. to melt them into a bundle foot, to shape them, or to size them.
In the unclamped state, the holding means also permit axial displacement of the bristles therein relative to one another to bring the useful ends of each partial group into different envelope surfaces. These surfaces may be curved in a smooth or non-smooth manner.
The method according to the invention permits the partial groups to be in close proximity to each other during formation of a bristle group and to be tightly packed together to form a bristle group with defined, bordering surfaces always being located between the partial groups.
In a preferred embodiment, the bristles of the partial groups are made from endless monofilaments by accommodating bristles of the same type, in the form of endless monofilament cords, on separate spools, removing the cords of bristles from the spools and introducing them into the guides to form one partial group each, wherein the bristles of all partial groups forming a bristle group are simultaneously supplied to the guides. The cords forming the partial groups may have different amounts of endless monofilaments.
The partial groups may also be made from short-cut bristles of appropriate length.
The invention further concerns a device for carrying out the method according to the invention. A device of this type forms a bristle group comprising at least two partial groups of different type bristles, by providing at least one spool with a cord of monofilaments having the same type of bristle, for each partial group, and with at least one drawing device, disposed downstream of the spool, with one guiding channel for each cord and, downstream of the drawing device, a stationary shaping device having a corresponding number of shaping channels whose openings facing the drawing devices are aligned with the guiding channels, wherein the opening thereof has a cross-sectional shape that varies into the partial cross-section of the partial group and simultaneously converges towards an envelope cross-section corresponding to the cross-section of the bristle group. A moveable holding means for the bristle group is advantageously disposed downstream of the shaping device having holding channels whose shape and arrangement correspond to those of the guiding channels of the drawing device facing same, wherein the cords can be removed from the spools by the linearly moveable drawing device, and can be pushed through the shaping device and optionally transferred to the downstream holding means, and further comprising a cutting device, disposed between the shaping device and the holding means, for cutting the bristle group, located in the holding means, to a desired length, wherein, the holding means with the bristle group can be moved for mounting the bristle group to the bristle support.
The device according to the invention cyclically produces the bristle groups, or the entire bristle stock, from several bristle groups which are then fastened to the bristle support or transported by the holding means to be fastened thereto.
The shaping channels of the shaping device can simultaneously taper in the direction of their cross-sectional variation such that the bristles of the partial group are simultaneously compressed during shaping.
In a preferred embodiment, at least two separately movable drawing devices are disposed one after the other, which, either individually or collectively, cooperate with the cords forming the partial groups to insert the partial groups into the holding means to the same or differing extents.
In this manner, partial groups of differing lengths can be easily made within one bristle group.
The drawing device and the holding means preferably comprise parallel layered plates, one of which is a clamping plate which can be moved transverse to the guiding or holding channels.
With the inventive device, the holding means with the clamped bristle group can be transported to a processing device and/or a device for treatment of the useful bristle ends and/or of the bristle ends which are to be mounted, before the bristle group or the bristle stock, consisting of several bristle groups, is fastened to the bristle support.
The method and device in accordance with the invention facilitate production of brushes having a bristle stock formed from bristle groups of defined cross-sectional shapes and having at least two partial groups of bristles of various types with complementary cross-sectional shape, wherein flat or curved bordering surfaces are formed between the at least two partial groups of a bristle group. Undefined mixing of the various bristle types is prevented and the partial groups are disposed within each bristle group in defined geometrical shape.
The at least one partial group of a bristle group may thereby surround the other partial group, e.g. two partial groups can be disposed concentric to one another. Several partial groups of a bristle group can also surround a central partial group in a concentric fashion.
The at least two partial groups of a bristle group can consist of bristles of various cross-sections, various cross-sectional shapes, various materials, various material compositions or material characteristics, various surface conditions or various colors.
A preferred embodiment provides that the partial group within a bristle group consists of bristles having a lower flexural strength that that of the bristles in the partial group(s) surrounding this partial group. In this way the inner, softer, e.g. thinner bristles are supported from all sides along at least part of their length.
In each bristle group of this embodiment, the partial group of the bristles having the lower flexural strength can protrude past the ends of the surrounding bristles having the higher flexural strength.
Bach bristle group can have the ends of partial group bristles disposed in flat, optionally differing envelope surfaces or in curved envelope surfaces and, optionally, in envelope surfaces of various curvatures.
The ends of the bristles of all partial groups of a bristle group are preferably disposed in a smoothly curved envelope surface which, in a further advantageous embodiment, is symmetric with respect to an axis extending parallel to the bristles of the bristle group.
The invention is described below with embodiments shown in the drawing.